USB 1.1/2.0 layout guild

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【文件名】:0635@52RD_SM320PCBLayoutGuidelines.pdf
【格　式】:pdf
【大　小】:89K
【简　介】:
【目　录】:



Placement and Routing
1. Place the USB 2.0 device and connector on the unrouted board first.
2. With minimum trace lengths, as equal as possible (D+, D-), route high-speed clock
and USB 2.0 differential signal pair first. Keep maximum distance between
high-speed signals to USB 2.0 differential signal pair.
3. Route the USB 2.0 differential signal pair on the component side, which is adjacent
to the ground plane layer. Vias to different signal trace layers or routing to close to
breaks in the ground plane will adversely affect the differential trace impedance.
4. Route USB 2.0 differential signal pair using a minimum of vias and corners. It can
reduce signal reflection and impedance change.
5. If it’s necessary to turn 90°, it’ better to use two 45° turn or an arc, instead of
making a single 90° turn. It can reduce reflection on the signal by minimizing
impedance discontinuities.
6. Please don’t route USB 2.0 differential signal pair trace under crystal, oscillator,
clock synthesizers, magnetic devices or ICs. It will cause interference.
7. Stubs on USB 2.0 differential signal pair should be avoided. While stubs exist, it will
cause signal reflection and affect signal quality. If a stub is unavoidable in the
design, no stub should be greater than 200mils.
8. Route USB 2.0 differential signal pair traces over continuous ground and power
planes. Avoid crossing anti-etch areas or any break in the underlying planes.
9. Avoid routing the USB 2.0 differential signal pair near the edge of the PCB or power
planes.
10. Keep parallelism between D+ and D- with the trace spacing, which achieves 90Ω
differential impedance.
11. Provide adequate trace width to handle the current requirements of power control
devices.